2.1. VISCOUS HYDROCARBONS
While large quantities of high-quality, relatively inexpensive, light crude oils presently are recoverable from world-wide geographical locations, ever-increasing consumption of petroleum fuels and other petroleum products and the energy crisis precipitated by such high demands have brought interest to bear on the enormous reserves of low-gravity, viscous hydrocarbons which also exist throughout the world. Viscous hydrocarbons present in natural deposits have been generally classified as viscous crude oils, bitumen or tar and have been variously called heavy crudes, native bitumen, natural bitumen, oil sands, tar sands, bituminous sands or deposits and natural asphalts, all of which materials are chemically gradational and nearly indistinguishable without standardized analyses. [For a discussion of the general characteristics of viscous hydrocarbons and the problem of precisely defining or classifying them, see Meyer, "Introduction" in: The Future of Heavy Crude and Tar Sands, p. 1, Mining Informational Services, McGraw Hill, Inc., New York (1981). See also Section 6.2 infra.]
The geograhphical distribution of heavy crude reserves is given in Table I [abstracted from Meyer and Dietzman (1981), "World Geography of Heavy Crude Oils," in: The Future of Heavy Crude and Tar Sands, pp. 16-28, Mining Informational Services, McGraw Hill, Inc., New York (1981)]. The total estimated figure for oil in place is 6200.times.10.sup.9 barrels. Venezuela heads the list with roughly half of this total, 3000.times.10.sup.9 barrels. Canada follows closey with 2950.times.10.sup.9 barrels (this total includes hydrocarbon in bitumen), while the United States has an estimated 77.times.10.sup.9 barrels. To put these figures in perspective, the total world reserves of oil lighter than 20.degree. API is estimated to be about 660.times.10.sup.9 barrels. Yet undiscovered reserves are estimated at 900.times.10.sup.9 barrels. Thus, heavy crude is more plentiful than conventional oil by about a factor of four. Further considering the amount of heavy residual oils that result from the processing of conventional crudes, the amount of heavy oils that exists worldwide is very great indeed.
TABLE I ______________________________________ WORLD HEAVY OIL DEPOSITS (Billions of Barrels) Resource Estimated Country In-Place Recoverable ______________________________________ Venezuela 3000 500 Canada 2950 213 United States 77 30 Italy 12 1 Madagascar 25 1 Iran 29 3 Iraq 10 1 ______________________________________
It is clear that reserves of conventional light crudes are being depleted much faster than heavy crudes and that development of world reserves of viscous hydrocarbons will eventually become necessary to support world petroleum demands. Significant production of heavy crudes has begun, primarily by steam-assisted enhanced recovery methods. For example, recent estimates place production of heavy crude oil in California at 250,000 barrels per day. Future estimates [Barnea, "The Future of Heavy Crude and Tar Sands," in: The Future of Heavy Crude and Tar Sands, pp. 13-15, Mining Informational Services, McGraw Hill, Inc., New York (1981)] project that by the year 2000, production of heavy oil plus the bitumen from tar sands will increase to one-third of the world's total oil production. Such rapid development of heavy oil resources will extend the petroleum era and should: (1) allow products from heavy crudes to benefit from the existing energy infrastructure; (2) assure fuel supplies to the transportation sector and feed-stock to petrochemical plants; (3) be a stabilizing factor for world petroleum prices, increasing the number of oil producing countries; ( 4) reduce the strategic and political aspects of oil production; and (5) postpone the need for massive investments in coal conversion and other facilities for synthetic oil production.
With regard to residual fuel oil, the recent trend in the United States has been a reduced demand for such materials. Consequently, refiners who can afford to have made sizable capital investments in cokers and other heavy end cracking processes to increase the production of light fractions from each barrel to crude. The result has been a decrease in residual oil production capacity and a decline in fuel quality.
Five years ago 1% sulfur residual fuel oils with API gravities of 17.degree. were common. The typical 1% sulfur residual oil today has an API gravity of 10.degree., and there has been increased availability of even lower gravity oils, including those with "negative gravity", i.e., API less than zero. Part of the reason for this change in quality has been the mix of crude oil slates being used by the refiners. With the wider application of tertiary recovery techniques, increased amounts of crudes from deeper wells, and the development of heretofore less desirable, i.e., heavier, reserves, the quality of crude oils can be expected to continue to decline. Eventually "sweet" high quality crude oils will probably be much more costly than heavier crudes and may cease to be available in large quantities.
Coupled with lower crude oil quality have been changes in refinery operations, wherein capacity has been added to increase the yield of the more profitable lighter fractions. To this end there has been increasing application of cokers, heavy oil crackers, visbreakers, and other processes. The end result is that there are fewer refiners with the capability of producing large quantities of high-quality residual fuel oil. Supporting this trend is the relative rarity of "straight run" residual fuel oils. With the quality of residual fuel oils on the decline, concerns have been raised regarding the ability to burn these and future residual oils in an environmentally acceptable manner. There is a clear need for developments which will make it possible to burn lower quality materials as cleanly as higher quality materials.